1. Field of the Invention
This invention relates to disc filters and more particularly to a fabricated central shaft of such disc filters.
2. Description of the Prior Art
Disc filter bags have long been used in conjunction with a rotatable central core for filtering taconite or other particulate slurries. The disc filter bag assembly rotates about the core to sequentially submerge successive filter bags in a slurry. A vacuum draws the slurry filtrate through the filter bags. The filter bags are operably connected to a conduit within the central core. The filtrate enters the conduit and is drawn out through the ends of the central core.
The use of powerful vacuum pumps creates problems when a filter bag tears. Unfiltered slurry containing iron ore fillings, coal particles or other industrial particulates is then forcefully drawn into the conduit and causes erosion and failure within the conduit. The erosion is particularly severe within a section of the conduit opposite the aperture leading to the filter bag.
Various modifications and improvements to the disc filter assembly have been sought to improve the reliability of the central core and to lessen the cost of the repair and replacement due to the wear and tear of the central shaft.
The conventional but unsatisfactory solution to the problem of erosion is to make the central core from a solid cylindrical piece of cast iron. The conduit passageways are radially placed around axis of the core with a substantially thick iron wall surrounding each conduit. The central area of the iron core is hollowed to provide a lighter weight iron core. When a conduit is eroded, the conduit is rebored a little wider. However, the erosion eventually eats away to the hollow central area of the core, causing a break in the conduit. The break in the conduit renders the conduit inoperative, and causes a general loss of vacuum efficiency.
Replacement of the eroded iron core is costly and time-consuming. Part of the high cost of replacing the iron core is due to the fine machining required to have different sections of the iron core aligned correctly with other sections so that they rotate around their axis without wobble. The time required to replace the iron core is great since the whole filter disc assembly must be disassembled and reassembled onto the new iron core.
Since replacement of the iron core is expensive and time-consuming, the eroded conduit would be plugged up at the point of erosion. At least one filter disc bag would become inoperative, since the plug would block any passage from the filter bag to the conduit. The iron core is used until a number of filter bags become inoperative due to a plurality of plugs sealing off major sections of the conduits. The economics of replacing an iron core demanded that a crippled iron core be used long beyond the point where the iron core is being used efficiently.
Various solutions to the erosion problem have been proposed. In the U.S. Pat. No. 3,659,716, issued to Peterson et al on May 2, 1972, certain of the problems were explicitly aproached. The Peterson et al patent discloses a filter disc central core assembly comprising a plurality of longitudinal pipes having a rectangular shape with reinforced surfaces on the opposite side of the apertures in the pipes. At the apertures of the rectangular pipes, removable castings are attached thereto. The castings have angled walls which receive the blasting force of the filtrate. The removable castings would have to be replaced at regular intervals of time. A combination of the reinforced surface opposite the aperture and the castings designed to receive the force of the flow is designed to increase the time interval before the necessary replacement of the center core.
Another proposed solution to ease the repairing cost is disclosed in the U.S. Pat. No. 2,894,632 issued to R. B. Myers on July 14, 1959. The Myers reference discloses modified filter segments integrally connected to a pipe segment which are rotatably mounted onto a central shaft. If the filter segment is ripped or the pipe segment is worn, only that section need be replaced. However, the invention disclosed in the Myers reference is not compatable to be incorporated in part with the conventional central cores and conventional disc filter bags.